Excess weight has been recognized as a major health problem, particularly in the industrialized nations. Another significant problem is high cholesterol levels in the blood stream. These problems are due in large part to consumption of more calories than are expended. Fats and oils are the most concentrated form of energy in the diet, with each gram supplying approximately nine calories. It has been estimated that fats constitute, on average in the U.S., about 40% of the total calories in the diet. The recommended level is less than 30% of total calories.
The sources of fats in the diet are many and varied. Such foods include baked products, candies, icings and frostings, salad dressings, shortening, butter, sour cream, margarine, peanut butter and other nut spreads and processed meats and meat analogs. A significant portion of the fat in these products is provided in the form of a liquid oil a solid fat or a shortening. It is desirable to reduce the levels of fat and calories in foods. It is also desirable to reduce the level of saturated medium and long chain (C.sub.12-20) fats, in contrast to unsaturated fats which are believed to be healthier. Fat level is best reduced with low or insignificant deleterious effects on the baking and cooking properties of the food, its taste, and its mouth feel characteristics.
Recently, the importance of adding fiber to the diet to lower blood cholesterol levels has been stressed. Adding fibers, even in finely ground or particulate form can give a gritty feel to the fat and make it taste "sandy" or lumpy. A fat replacement which would add fiber to the food in a manner which is not gritty or palpable is also desirable.
One way to add fiber and water to fat is through a gel. The addition of both fiber and water lowers the calories of the food since they ordinarily replace higher calorie ingredients such as starch, sugar and fat. Gels made from polysaccharides and polar solvents, while not being gritty, do not mix well with edible fat and, consequently, tend to remain in clumps or droplets of gel in solid fats. Gels can also taste slimy. Also, for gels in general, a relatively high degree of syneresis can occur over time, thereby resulting in a separate liquid phase. This liquid phase may not be miscible with certain product compositions.
A second way of adding fibers or polysaccharides to a food is through microparticulation of a gel. Microparticulation requires extensive processing to keep the microparticulated fiber or polysaccharide in a form which will remain separated in the food; i.e. it does not coalesce.
Other ways of incorporating water and synthetic fats have been through the use of emulsifiers which make water in oil or oil in water emulsions. Emulsions are made of two immiscible liquids. These emulsions can break down during the cooking or baking of the product and also can separate during storage.
It has now been discovered that certain liquid crystals, i.e., polymer liquid crystals can be made which incorporate (fiber) polysaccharides, water and fat into foods.
The liquid crystalline state exists between the boundaries of the solid phase and the isotropic liquid phase (i.e. an intermediate between the three dimensionally ordered crystalline state and the disordered dissolved state). In this state some of the molecular order characteristics of the solid phase are retained in the liquid state because of the molecular structure and short range intermolecular interaction. The ability of some compounds to form a liquid crystalline mesophase had been observed nearly a century ago. Since that time many compounds exhibiting liquid crystalline properties have been synthesized. D. Sek: Structural variations of liquid crystalline polymer macromolecules; Acta Polymerica, 39 (1988) Nr. 11, p.599.
Low molecular weight organic surface active compounds (emulsifiers) are distinguished from polymers. The latter comprise large molecules made up of repeating units while the former are low molecular weight compounds. Physically and chemically, these two subclasses of materials are different from each other.
Low molecular weight liquid crystals, i.e. liquid crystals formed from a low molecular weight emulsifier or organic amphiphile (a compound having both a polar and a non-polar group, as a soap or long chain fatty acid monoglyceride) are metabolized and therefore contribute calories. Also, because of their weight, they are added at higher concentrations to achieve the same functionality as polymer liquid crystals. On the other hand, polymer liquid crystals are made of a polymer and a solvent. The polymers can be a long chain of repeating units of amphiphiles or polymerized low molecular weight materials. They also form different types of liquid crystals.
In the literature, liquid crystals are also referred to as anisotropic fluids, a fourth state of matter, polymer association structure or mesophases. Those terms are used interchangeably. The term "polymer liquid crystals" as used herein means "polymeric lyotropic liquid crystals" unless otherwise specified. The term "lyotropic" means a liquid crystalline system containing a solvent. This type of liquid crystal is distinguished in the art from thermotropic, heat, and magnetically induced liquid crystals. Suitable polymers can have either a non-amphiphilic or an amphiphilic structure. The same compound can form lyotropic and thermotropic liquid crystals. Lyotropic liquid crystal systems also can show thermotropic behavior.
A general description of the phase behavior of a soluble polymer in a solvent is as follows: (I) The polymer dissolves in the solvent to form an isotropic polymeric solution. (II) When the concentration of the polymer increases, a mixture of isotropic polymeric solution+liquid crystals is formed. (III) When the level of the polymer increases further and the required mixing is applied, a homogeneous single-phase liquid crystal range is induced. (IV) When even more polymer is present, a mixture of liquid crystals and crystalline polymer forms. (V) When extremely large amounts of polymer are present a crystalline and/or partially crystalline phase are present.
It is important to understand that liquid crystals are substances that possess mechanical properties resembling those of fluids yet are capable of transmitting polarized light (birefringence) under static conditions. In some cases they may show Bragg reflections characteristic of a well-defined molecular spacing. They have high degrees of orientational order and chain extensions.
Polymeric lyotropic liquid crystals are subdivided into three subclasses: I. nematic, II. cholesteric, and III. smectic, which are optically anisotropic. See J. H. Wendorff. in "Scattering in Liquid Crystalline Polymer System" in "Liquid Crystalline Order in Polymers," A. Blumstein (ed.), Academic Press, Chapter 1 (1978).
I. In the nematic liquid crystalline phase the centers of gravity of the polymeric particles are arranged at random, consequently no positional long range order exists. Within volume elements of a macroscopic sample, the axes of all particles are oriented in a specific direction. Near the smectic-nematic transition temperature, there may be an additional ordering (positional order).
II. The cholesteric liquid crystalline phase is often thought of as a modification of a nematic phase. since its molecular structure is assumed to be similar to the latter. No positional order but only an orientational order exists in the cholesteric phase. In contrast, however, to the nematic phase, the cholesteric phase is characterized by the fact that the direction of the long axes of the molecules change continuously within the sample. This leads to a twist about an axis perpendicular to the long axes of the molecule.
III. In the smectic phases the centers of gravity of the elongated molecules are arranged in equidistant planes and smectic layers are formed. The planes are allowed to move perpendicularly to the layer normal and within the layers different arrangements of the molecules are possible. The long axes of the molecules can be parallel, normal or tilted with respect to the layer. A two-dimensional short range order or a two-dimensional long range order can exist within the smectic layers. The smectic modifications are labeled according to the arrangement of the particles within the layers.
Investigations of miscibility between different liquid crystalline modifications allow the distinction between various smectic phases and between smectic, cholesteric and nematic phases.
The light microscopy of liquid crystals is described in The Microscopy of Liquid Crystals, Norman Hartshorne, Microscopy Publications, Ltd., Chicago, Ill., U.S.A., 1974. Birefringence occurs in general for mesomorphic states. Methods for microscopic observation and evaluation are discussed in Chapter 1, pp. 1-20, and cholesteric mesophas (liquid crystal) systems are discussed in Chapter 6, pp. 79-90. A preferred method for determining occurrence of liquid crystals is by observing birefringence of thin liquid crystal films between glass slides or from thin slices of a material under a polarizing microscope.
Focusing on the polymeric lyotropic liquid crystals of the present invention, in general, they are prepared by mixing the polymer with a sufficient amount of a solvent within the critical concentration and temperature ranges. The polymeric liquid crystalline phase flows under shear and is characterized by a viscosity that is significantly different from the viscosity of its isotropic solution phase. In other words, for some polymers, as the concentration increases, the viscosities of the polymer/solvent mixture increases until it reaches a viscosity peak. Then the viscosity decreases dramatically. The presence of such viscosity peaks signifies the onset of, or the presence of, a polymeric lyotropic liquid crystalline order. Hence, liquid crystals are distinguishable from polymeric systems which are isotropic solutions, pure solids, simple mixtures of solids and liquids and rigid isotropic polymeric gels. Rigid gels do not flow under shear like liquid crystals. Also, when viewed with a polarized light microscope, liquid crystals show identifiable birefringence, as, for example, planar lamellar birefringence, whereas when isotropic solutions and rigid gels are viewed under polarized light, both show dark fields.
Liquid crystal xanthan gum (a polymer) is reported to stabilize an oil-in-water emulsion (Biological Abstract 79:12413. Food Research Institute, Norwich, U.K. and M. Hennock et al., J. Food Sci., 49, 1271, (1984). However, specific applications in foods are not disclosed.
Adding isotropic solutions of the polysaccharide in polar solvent to a fat would lead to unacceptable results. If the polysaccharide were soluble in the solvent, it would not be gritty, but the solvent nevertheless would not mix well with the fats. The solution would be expected to separate from the fat during storage or use. Flowable polysaccharide liquid crystals, on the other hand, allow substantial amounts of polysacchride to be incorporated in a fat. Such mixtures can substitute for fats in a variety of edible, fat-containing products without suffering the drawbacks of non-liquid crystal technology, i.e. gritty taste, separation or syneresis.
It is an object of this invention to provide edible compositions containing a fat replacement for all or part of the fat in a food product without significant deleterious effect on the cooking, taste, or mouth feel characteristics of foods made with this fat replacement.
It is particularly desirable that the fat substitute composition be made from ingredients that are presently used and approved for use in edible product applications. approved for use
It is also an object of this invention to provide a fiber additive to the food without affecting the mouth feel and taste of the product.
It is also an object of this invention to provide a fat substitute which can be made with a minimum of processing and which is easily mixed with the food.
It has now been found that the above objects, as well as other benefits, can be attained by substituting liquid crystals formed from polysaccharides and solvents for fat conventionally present in certain foods.